Hydraulic fracturing is an effective method of increasing hydrocarbon production. The method involves pumping of a fracturing fluid into a subterranean formation (i.e. reservoir) through a wellbore under a pressure exceeding the formation stress. A propping material is placed in the resulting fractures to prevent them from closing, which, thus, provides unimpeded flow paths and enhanced transport of hydrocarbons from the reservoir to the wellbore.
The art of hydraulic fracturing is based to a great extent on materials: the fluids with their various constituents and the proppants with optional auxiliary particulates. The proppant materials are intended to provide enhanced hydraulic conductivity of a fracture under the formation closure stress. Proppant design is focused on several material characteristics that include: a) compressive strength or crush resistance under formation closure stress, to avoid generation of fines, which are known to damage proppant pack conductivity; b) low specific gravity, to place the proppant deep into a fracture with a fluid of reasonable viscosity; c) substantially spherical proppant particulate shape with smooth particle surface and uniform size distribution to maximize proppant pack permeability; and d) low material cost. There is usually a trade-off between the properties. As an example, proppant crush resistance, which is a characteristic of material mechanical strength, often conflicts with the required proppant low density and low cost. The choice of proppant also strongly depends on the properties of the targeted reservoir, which can vary significantly. Therefore, while proppant pack conductivity is often considered as a primary proppant characteristic, in certain cases, it can be sacrificed to achieve other benefits. In very tight reservoirs, even very low fracture conductivity will still result in a suitable flow path for hydrocarbons entering from the formation.
It would be desirable to have an inexpensive proppant that is readily transported deep into fractured formations by low viscosity fluids and need not have low specific gravity, particle size or shape uniformity, or strength.